Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.3.44 (P-glycoprotein)
 13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Many cancers have been cured by chemotherapeutic agents. However, other cancers are intrinsically drug resistant, and some acquire resistance following chemotherapy. Cloning of the cDNA for the human MDR1 gene (also known as PGY1), which encodes the multidrug efflux protein P-glycoprotein, has made it possible to measure levels of MDR1 RNA in human cancers. We report the levels of MDR1 RNA in greater than 400 human cancers. MDR1 RNA levels were usually elevated in untreated, intrinsically drug-resistant tumors, including those derived from the colon, kidney, adrenal gland, liver, and pancreas, as well as in carcinoid tumors, chronic myelogenous leukemia in blast crisis, and cell lines of non-small cell carcinoma of the lung (NSCLC) with neuroendocrine properties. MDR1 RNA levels were occasionally elevated in other untreated cancers, including neuroblastoma, acute lymphocytic leukemia (ALL) in adults, acute nonlymphocytic leukemia (ANLL) in adults, and indolent non-Hodgkin's lymphoma. MDR1 RNA levels were also increased in some cancers at relapse after chemotherapy, including ALL, ANLL, breast cancer, neuroblastoma, pheochromocytoma, and nodular, poorly differentiated lymphoma. Many types of drug-sensitive and drug-resistant tumors, including NSCLC and melanoma, contained undetectable or low levels of MDR1 RNA. The consistent association of MDR1 expression with several intrinsically resistant cancers and the increased expression of the MDR1 gene in certain cancers with acquired drug resistance indicate that the MDR1 gene contributes to multidrug resistance in many human cancers. Thus, evaluation of MDR1 gene expression may prove to be a valuable tool in the identification of individuals whose cancers are resistant to specific agents. The information may be useful in designing or altering chemotherapeutic protocols in these patients.
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PMID:Expression of a multidrug resistance gene in human cancers. 256 56

A spontaneously originated murine mammary adenocarcinoma (16C), selected for its sensitivity to agents active against breast cancer in women, and one of the very few experimental solid tumor models responsive to Adriamycin (ADR) was used to study the mechanism of induced ADR resistance in vivo. A resistant variant of the tumor was obtained from the explant of a regrown tumor following a dose of ADR (12 mg/kg) that caused complete tumor repression but not cure. Progressive refractoriness to ADR was observed following up to six repeated cycles of treatment, regression and regrowth. However, beyond the sixth treatment, no further degree of resistance could be obtained. The cell line so established, designated 16C/ADRR, has a glutathione (GSH) content 1.67 times greater than the parent 16C line. Depletion of GSH by buthionine sulfoximine (BSO) enhanced the cytoxicity of ADR in both cell lines. The sensitization effect appeared to be dependent on the degree of GSH depletion, requiring a threshold level of depletion to approximately 30% of control. The resistance of 16C/ADRR, however, appeared not to be directly related to the increased absolute GSH level per se since reduction of the GSH content of the 16C/ADRR line to levels similar to that of the parent 16C line did not restore the original sensitivity to ADR. However, the activities of two important elements in the GSH detoxification system, GSH peroxidase and S-transferase, were found to be elevated in resistant cells by factors of 2.4 and 4.7-5.6 respectively. In vivo studies with a diverse spectrum of antineoplastic drugs revealed a pattern of cross-resistance consistent with the idea that elevated GSH S-transferase and peroxidase activities may be responsible for the decreased (2.8- to 5.3-fold) sensitivity to ADR. 16C/ADRR exhibited cross-resistance with melphalan (MEL), but none with vincristine (VCR), vinblastine (VBL) or etoposide (VP-16). These results clearly demonstrate non-adherence by the 16C/ADRR tumors to the well characterized multidrug resistance (mdr) phenotype. Further affirmation of this conclusion was obtained by immunochemical and pharmacological studies. When a monoclonal antibody prepared against the mdr associated, 170 kD P-glycoprotein (170 P-gp), was used, the presence of the 170 kD P-gp in both the sensitive and resistant 16C lines could not be detected, although the presence of a lower molecular weight form of P-gp could not be ruled out entirely. High performance liquid chromatographic measurement of ADR accumulation and elimination also failed to reveal any significant differences between the sensitive and resistant variants.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:A study of the mechanism of resistance to Adriamycin in vivo. Glutathione metabolism, P-glycoprotein expression, and drug transport. 257 74

We examined the distribution of RNA levels expressed by the multidrug-resistance gene (MDR1, also known as PGY1) in 42 renal cell carcinoma (RCC) samples (38 primary and four metastatic lesions). The median MDR1 RNA level for the 38 primary lesions, expressed relative to the level for KB-3-1 cells, was approximately one-half of the level in multidrug-resistant KB-8-5 cells. Elevated MDR1 RNA levels were also observed in three of the four metastatic lesions. The mean MDR1 RNA level was higher in well-differentiated RCCs than in those that were poorly differentiated, suggesting that the increased expression of the MDR1 gene in RCCs originates from the increased expression in renal proximal tubule cells. To clarify the association of the MDR1 protein product P-glycoprotein with natural resistance to doxorubicin (ADR) in RCCs, we evaluated the effects of quinidine on in vitro sensitivity to ADR in 16 RCC samples, using a [3H]thymidine incorporation assay. The enhancing effect of quinidine (7.5 micrograms/mL) on sensitivity to ADR was statistically significant only in the group with high MDR1 RNA levels. Similar enhancement by quinidine of sensitivity to ADR was also observed in the established RCC cell lines in which MDR1 RNA levels were high. These results suggest that P-glycoprotein is active in the natural resistance of RCCs to ADR.
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PMID:MDR1 RNA levels in human renal cell carcinomas: correlation with grade and prediction of reversal of doxorubicin resistance by quinidine in tumor explants. 272 49

In a cell fusion experiment with multidrug resistant (MDR) mouse SEWA tumor cells and sensitive Chinese Hamster CHO cells, the resistant hybrid cells were completely without recognizable mouse chromosomes. Instead, numerous chromatin bodies (CB) were found that contained copies of a high molecular weight P-glycoprotein gene (PGY1) associated with the MDR condition. The present paper reports on the CB under long-term selective and nonselective growth. The CB were of a stability intermediate between that of double minutes (DM) and homogeneously staining regions (HSR). The stability of the CB was different in the two hybrid lines studied.
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PMID:The semistability of centric chromatin bodies during long-term passage of multidrug resistant mouse-Chinese hamster cell hybrids. 338 36

P-glycoprotein (P-gp/P-170), a transmembrane efflux pump known to be one of the mechanisms responsible for multidrug resistance in cancer therapy, is constitutively expressed in several solid human tissues as well as in normal peripheral blood lymphocytes and bone marrow cells. In particular, this molecule has been associated with the transport of perforin and other cytolysins in natural killer (NK) and T cytotoxic lymphocytes. In the present study, we analyzed peripheral blood lymphocytes (PBLs) from controls and HIV+ patients for phenotypic expression and function of the P-gp/P-170 molecule. We found that 90% of all PBL subsets (i.e., CD4+, CD8+, CD56+, and CD19+ cells) expressed surface P-gp/P-170 both in controls and HIV+ patients. However, a significant decrease in CD4+/P-170+ and CD19+/P-170+ cells was observed in HIV+ individuals with respect to controls. PHA and IL-2 stimulation of PBLs was unable to increase the expression of P-gp/P-170 both in controls and HIV+ patients, despite the increased detection of the CD25 molecule. On the other hand, stimulation with anti-CD3 determined a significant increase in lymphocyte P-gp/P-170. The function of P-gp/P-170, assessed by a flow cytometric assay for rhodamine-123 (Rh123) efflux, was significantly reduced in CD16+ NK cells and CD19+ B cells from HIV+ patients. The Rh123 efflux by NK cells correlated (p < 0.01) with the NK cytotoxicity against the 51Cr-labeled K562 cell line. Last, the effect of the antiretroviral drugs AZT, ddI, and ddC on P-gp expression and function was evaluated. The dideoxynucleoside compounds did not inhibit P-gp/P-170 function of normal mononuclear cells in vitro, and did not increase P-gp/P-170 expression in vivo, in patients undergoing antiretroviral therapy with AZT. These findings provide further evidence of a possible involvement of the P-gp/P-170 system in specific immunological lymphocyte functions, and especially in cytotoxic-type functions. In addition, it is possible to suggest, on the basis of our experimental data, that the dideoxynucleoside class of antiretroviral agents does not contribute to the phenotypic and functional alterations related to P-glycoprotein during HIV infection.
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PMID:Transmembrane P-glycoprotein (P-gp/P-170) in HIV infection: analysis of lymphocyte surface expression and drug-unrelated function. 749 36

Calphostin C is a potent and specific inhibitor of protein kinase C (PKC). In this investigation we examined the effect of Calphostin C (without prior exposure to light) on daunorubicin (DNR) accumulation and sensitivity to DNR in multidrug-resistant (MDR) murine leukemia P388/ADR and human myeloid leukemia HL60/AR cells. P388/ADR cells overexpress P-glycoprotein, whereas HL60/AR cells lack any expression of P-glycoprotein (both at mRNA and protein levels). Calphostin C, in a concentration-dependent manner, increased the accumulation of DNR in P388/ADR cells and partially reversed (threefold) the DNR resistance in P388/ADR cells but had no effect on either of the parameters in HL60/AR cells. Calphostin C-induced increased accumulation of DNR in P388/ADR cells was due to increased uptake and decreased efflux of DNR. Furthermore, Calphostin C increased the uptake and decreased the efflux of rhodamine 123 (a substrate for P-gp) in P388/ADR cells but had no such effect in P388 cells. In addition, Calphostin C without exposure to light did not inhibit PKC activity in any of the cell lines studied. Taken together, these data suggest that Calphostin C may reverse drug resistance via P-glycoprotein independently of its effect on PKC activity. Therefore, any data regarding the effect of Calphostin C on the reversal of MDR should be interpreted in the light of these findings.
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PMID:Effect of Calphostin C (PKC inhibitor) on daunorubicin resistance in P388/ADR and HL60/AR cells: reversal of drug resistance possibly via P-glycoprotein. 751 83

During the past few years it has become apparent that simultaneous resistance of tumour cells to a number of heterocyclic drugs (multidrug resistance) is often correlated with overexpression of a P-glycoprotein (P-gp or P-170). P-gp expression can be studied by molecular biology and immunohistochemical techniques. The latter provide a rapid, sensitive and specific screening method suitable for testing even a relatively small number of tumour cells like those obtained at biopsy. The aim of this study was to detect and localize the immunohistochemical expression of P-gp in normal and neoplastic gastrointestinal tissue using the Mab JSB-1 in formalin-fixed paraffin-embedded specimens. A particularly striking finding of our study was the consistent, prevalent higher expression of P-gp in the stomach than in the colon, with a higher percentage of immunostaining in normal than in neoplastic tissue. This is in agreement with the fact that not only is the prognosis known to be worse for stomach cancer, but also the response to treatment is lower. Further studies should be carried out to verify the possibility of making routine tests of this kind for the evaluation of multidrug resistance, to guide the selection of patients for treatment of cancer with chemotherapeutic drugs.
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PMID:P-170 glycoprotein expression in gastric and colorectal carcinomas and normal mucosa. An immunocytochemical study. 754 88

Multidrug resistance, mediated by the P-glycoprotein 170 transport pump, is a serious problem in multiple myeloma. In this review we discuss the expression of P-gp as a differentiation antigen on normal T and B lymphocytes. In myeloma, circulating presumptively malignant B cells express P-gp prior to chemotherapy. A variety of evidence characterizes these circulating B cells as members of the malignant clone in myeloma, including the demonstration that they share immunoglobulin heavy chain (IgH) rearrangements with bone marrow plasma cells, and their extensive DNA aneuploidy. In some patients the only components of the clonal populations that express P-gp are the circulating B cells suggesting that they represent a reservoir of multidrug resistant cells that maintain malignant growth and spread in myeloma. We speculate that exposure to chemotherapy alters clonal homeostasis and exerts positive selection pressure on generative components of the myeloma clone. Thus the possibility exists that chemotherapy perpetuates rather than eradicates myeloma stem cells. P-gp is detectable on bone marrow plasma cells in myeloma but appears to be in an inactive form that is unable to mediate efflux of marker dyes. A similar phenomenon is seen for normal human monocytes which have surface P-gp but lack any functional export of P-gp substrates. P-gp appears to vary depending in a cell-type specific manner suggesting that it may be feasible to design inhibitors of P-gp which selectively block P-gp export by malignant cells and spare the function of P-gp on normal tissue, including lymphocytes and normal hematopoietic stem cells.
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PMID:Intrinsic expression of the multidrug transporter, P-glycoprotein 170, in multiple myeloma: implications for treatment. 754 27

Transfer of the human multidrug resistance 1 (MDR1) gene to hematopoietic stem cells offers an approach to overcome the myelosuppression caused by a number of antineoplastic drugs. This study was designed to determine the effect of MDR1 gene transfer on overall P-glycoprotein (P-gp) expression in murine hematopoietic cells. Mice were transplanted with bone marrow cells infected with either of two different MDR1 retroviral vectors. A reverse-transcriptase polymerase chain reaction-based assay was used to quantify expression levels of both endogenous and vector-derived P-gp encoding transcripts in hematopoietic cells of transplanted mice. Expression of both a truncated and full-length MDR1 mRNA species was noted in bone marrow and spleen colony cells. The truncated message resulted from cryptic mRNA splice sites within the MDR1 cDNA and was detected with both vectors. Full-length message levels exceeded those from the endogenous genes in all but one case and roughly approximated that seen in the modestly drug-resistant cell line SW620. We conclude that transfer of MDR1 retroviral vectors resulted in a significant increase in P-gp expression in most cases; however, aberrant splicing of MDR1 transcripts can result in reduced expression of vector-derived P-gp.
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PMID:Expression of retroviral vectors containing the human multidrug resistance 1 cDNA in hematopoietic cells of transplanted mice. 760 85

Multidrug resistance phenotypes in human tumours are associated with the overexpression of the 170 kDa P-glycoprotein encoded by the multidrug resistance 1 (MDR1) gene, and also with that of the non-P-glycoprotein-mediated multidrug resistance gene, MRP, which encodes a 190 kDa membrane ATP-binding protein. We have previously reported that overexpression of MRP appears to be responsible for spontaneous multidrug resistance in some human glioma cell lines (Abe et al., Int. J. Cancer, 58, 860-864, 1994). In this study, we investigated whether chemosensitising agents of P-glycoprotein-mediated multidrug resistance such as verapamil, a biscoclaurine alkaloid (cepharanthine), and a dihydropyridine analogue (NIK250) could also reverse multidrug resistance in human glioma cells. The glioma cell lines were the two MRP-expressing cell lines, T98G and IN500, an MDR1-expressing cell line, CCF-STTG1, and the MRP1 MDR1-non-expressing cell line, IN157. Verapamil and NIK250 almost completely reversed drug resistance to vincristine, etoposide and doxorubicin in T98G cells, while they also reversed drug resistance to vincristine and etoposide, but only partially to doxorubicin in IN500 cells. Cepharanthine as well as verapamil and NIK250 reversed vincristine resistance in CCF-STTG1 cells, but cepharanthine only partially reversed drug resistance in T98G and IN500 cells. The cellular accumulation of [3H]etoposide increased about 2- and 3-fold compared with control in T98G cells in the presence of verapamil and NIK250 respectively. Furthermore, the release of doxorubicin from the nuclei of T98G cells was blocked by NIK250. However, NIK250 and verapamil caused no apparent increase in vincristine accumulation in T98G cells. NIK250 or verapamil might exert inhibitory effects upon MRP function, resulting in a reversal of MRP-mediated spontaneous multidrug resistance in cultured human glioma cells.
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PMID:Chemosensitisation of spontaneous multidrug resistance by a 1,4-dihydropyridine analogue and verapamil in human glioma cell lines overexpressing MRP or MDR1. 764 Feb 27


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